For me it's Diablo II. Granted I've played my fair share of D2 since launch, and also recently on a private server with a comrade from hexbear, but I still feel like years later the game didn't grab me as much as D1 did.
Granted I don't hate D2, but for a game that I keep coming back to, D1 takes the prize.
A smaller Elden Ring would have been a less bad game but also a considerably less good one. When I played through that game at release I had absolutely no idea where the edges of that gameworld were, and it allowed me to be lost in it in a way no other game has managed to. I'd not trade that feeling for any amount of replayability.